1. Field of the Invention
The present invention relates to a recording sheet package for use with a printer, and a recording sheet supplying method. More particularly, the present invention relates to a recording sheet package for use with a printer in which positioning of stacked recording sheets is stabilized, and a recording sheet supplying method.
2. Description Related to the Prior Art
There are two types of thermal printer, including a direct thermal printing type and a thermal transfer type, for each of which recording sheet of a predetermined type is used. The recording sheet for the direct thermal printing is constituted by a support and three thermosensitive coloring layers overlaid thereon, which are cyan, magenta and yellow coloring layers. Heat energy of three values is applied to the recording sheet to develop colors of each of the coloring layers. Each coloring layer after being heated is optically fixed prior to thermal recording of a succeeding one of the coloring layers. For this optical fixation, ultraviolet rays of a predetermined range of the wavelength are applied to the recording sheet to destroy the coloring ability of each coloring layer. The succeeding coloring layer can be safely heated without influencing the density of the color developed in the preceding coloring layer. If the recording sheet of the direct thermal printing type is kept subjected to light from lamps as widely used appliances for light source, the coloring ability of the recording sheet is remarkably influenced. Consequently a stack of recording sheets is contained in a light-tight packaging bag, and furthermore contained in a cardboard box to be shipped commercially.
There are two types of thermal transfer printer, including a wax-transfer type and a sublimation type. The wax-transfer printer melts or softens ink of ink film, and transfers it to the recording sheet. The sublimation printer sublimates or disperses dye of ink film on to the recording sheet. The recording sheet for the wax-transfer printer consists of coat paper having high smoothness. The recording sheet for the sublimation printer consists of paper coated with polyester resin. For both of the thermal transfer printers, a plurality of recording sheets are stacked and contained in a moisture proof bag, which is then contained in a cardboard box to be shipped for sale.
A recording sheet package is used for easy handling of a stack of the recording sheets. To load the printer with the recording sheets, at first a packaging bag is opened to remove the recording sheet package, which is inserted in a sheet supply cassette. The sheet supply cassette is set in the printer. So the loading of the recording sheets is complicated to most of the users. While a user manually removes the recording sheets from the packaging bag, it is likely that the recording sheets are exposed to ambient light and touched by the user's hand. In the case of the recording sheets for the thermal transfer printing, touched portions are discolored by fingerprints. In the case of the recording sheets for the direct thermal printing, the coloring ability of the uppermost one of the recording sheets is influenced by the ambient light.
JP-A 5-116774 discloses the recording sheet package in which the recording sheets are not touched directly by user's hand, and with which the printer can be easily loaded with the recording sheets. A cutting line with a train of perforations is formed in a body of the recording sheet package. A portion of the body of the recording sheet package is cut away by tearing the cutting line, to form an opening for removal of the recording sheets. The tearing requires a user's manual operation prior to the loading into the printer.
It is likely that a user erroneously orients the recording sheet package to be inserted in the sheet supply cassette or in a printer, with the upper side of the recording sheet package directed downwards or with the front side directed backwards. When the upper side of the recording sheet package is directed downwards, printing heat is applied to the back surface reverse to the recording surface. No image is obtained in an acceptable manner, to waste the recording sheets. Particularly in the printer of the direct thermal printing, heating of the back surface causes damages to an array of heating elements of a thermal head.
It is possible to detect errors in loading of the recording sheets if the printer is provided with a sensor for detecting a recording surface and a back surface of the recording sheets. However such a sensor considerably raises a manufacturing cost of the printer. The loading with an error must be finished before the error can be detected. Thus operation of removal of the sheet supply cassette prior to the reloading is inevitable, and lowers efficiency in the loading.
Relative to the inner surface of a packaging body of the recording sheet package, the recording sheets become free in the course of a decrease of the remainder of the recording sheets. Curling tendency may occur in the recording sheets. If the packaging body containing the remainder of the recording sheets is removed from the sheet supply cassette, the recording sheets are likely to drop out of the packaging body to be damaged as the recording sheets are free.
A lifter lever opening is formed in a bottom wall of the recording sheet package according to the prior art in addition to a roller inserting opening for the supply roller. A lifter lever raises the recording sheets through the lifter lever opening to press the uppermost one of the recording sheets against the supply roller. The existence of the lifter lever opening is likely to cause entry of dust, ambient light or moisture into the recording sheet package after removal from the sheet supply cassette. Thus a problem is caused by the lifter lever opening in the low performance in shielding light and moisture.
The stack of the recording sheets are tightly contacted by the packaging body while contained in it. It is difficult in manufacturing the recording sheet package to use a method of inserting the recording sheets into the packaging body. It is general to manufacture the recording sheet package by wrapping the recording sheets with a packaging. The tight contact of the packaging body with the recording sheets causes high resistance to the advance of the recording sheets, to lower the smoothness in the supply of the recording sheets. Should the recording sheets be loosely contained in the packaging body with a space, the recording sheets are not positioned stably in the packaging body. Problems occur in the printing, as the recording sheets may advance obliquely or may be jammed.